Many syringes in common use today utilize a glass or plastic pre-filled cartridge. Such cartridges are conventionally sealed at one end by a rubber stopper and at the other end by a rubber membrane which is sealed against the outside of the cartridge by a metal cap. The metal cap is crimped onto the end of the cartridge thus ensuring an effective seal at the end of the cartridge remote from the rubber stopper. One example of such a syringe is described in AU-A-73632/81.
Cartridges of the type described are conventionally filled with an injectable medium and may then be autoclaved to ensure the sterility of the contents. In use, these cartridges are inserted into a syringe holder designed to allow expression of the contents of the cartridge. For example, metal barrelled syringes having a fitting at one end to accept a double sided needle and a plunger at the other end have previously been in use. These syringes are intended for multiple use and must be stored in a sterilizing cabinet after each use. Furthermore, they suffer from the disadvantage that they are heavy and large. The size of the syringe is a particular disadvantage as these syringes are intimidating for patients. Also in use are disposable syringe bodies to which there is fixed a double sided needle. When these disposable syringe bodies are used a pre-sterilized cartridge is inserted into the syringe body. The double sided needle is adapted to puncture the rubber membrane at the end of the cartridge barrel and a plunger rod is used to expel the contents of the cartridge.
The cumbersome nature of prior syringe assemblies has lead to various alternative assemblies being investigated with a particular view to designing a simple disposable syringe and cartridge. For example, in Australian patent specification 468,624 there is described a disposable syringe assembly having a barrel molded from a plastics material. This syringe however continued the use of double ended needles and required the use of an external shell for the mounting of the cannula. An alternative arrangement also using a double ended needle is disclosed in AU-A41625/78. This syringe assembly utilized a double ended needle encased within a housing which was retained in a hub socket within which the needle housing was adapted to move. On the application of an inward force on the needle housing a diaphragm adjacent the hub was punctured by the rearward needle to reveal the contents of the cartridge for injection. This development also suffered from the disadvantage of having to provide an internal diaphragm within the cartridge and the use of a double ended needle. Similar use of a puncturable diaphragm in conjunction with a spike for revealing the contents of a pre-filled syringe can be seen by reference to AU-A27579/77. It has also been common practice to utilize a needle guard and these guards have usually conveniently slipped over the needle fitting (for example see FIG. 1 of AU-B86910/82). Such needle guards are usually frictionally fitted over the needle fitting. In WO86/03126 there is disclosed a syringe which incorporates a retaining clip to hold a separate needle fitting in position over the end of an injection body having a specially moulded needle fitting seat. The retaining clip incorporates a protective sheath which is frangibly connected to the body of the clip. However, the syringe assembly described in W086/03126 suffers from the disadvantage of requiring a specially moulded seat for retaining the hypodermic needle fitting and a retaining clip to hold the needle in place. This limits use of the syringe to needles which can be fitted into the moulded seat and sealing requires the use of a separate sealing ring.